Radio devices can be equipped with both Bluetooth and broadband wireless technologies such as WiMAX or LTE which are used by 4G networks, Several common usage cases require the simultaneous operations of co-located, Bluetooth (BT) and LTE/WiMax radios, such as the use of a BT headset on a cellular phone using LTE communications.
BT and LTE/WiMax operate in adjacent bands, causing mutual interferences. In order to coexist together, the BT transactions should be synchronized to the LTE/WiMax frames, in a way where both TX and RX of the two technologies are performed simultaneously.
The problem is to allow coexistence of these two wireless technologies. The reason they cannot coexist is that they use adjacent frequencies which are close to each other in the frequency domain, which block each other. When one transmits, the other cannot receive, and vice-versa. The fundamental issue is that both technologies use very, very close frequency bands and they have coexistence issues. The LTE, which is cellular technology, uses band 40 and band 7, which are closely adjacent to the BT band. As the LTE and BT bands get close to each other, the co-existence problems increase. The problem is to make these two technologies work together.
To address this problem, the Bluetooth Special Interest Group (BT SIG) has defined two ways to adjust the Bluetooth network clock (BT CLK) that controls timing of network communications while in active connection. First, new devices (that is, according to the next Bluetooth standard after the BT 4 specification, commonly referred to as BT Core 4.1 or further) will use a new dedicated BT command. Second, legacy devices (that is, according to the current BT 4 specification or earlier) can drift the BT network clock for a long period up to the required BT CLK change.